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54 Cards in this Set
- Front
- Back
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With digital sensors and plates, what do the xrays interact with?
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electronic detectors
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What has higher radiation sensitivity, digital or radiographic films?
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digital sensors and plates have higher radiation sensitivity
radiographic film has low radiation sensitivity |
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Advantages of digital imaging
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reduction in radiation by 60-90%
pt education increased diagnosis short exposure time elimination of darkroom elminate hazardous chemicals remote consultaion capibility |
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What are disadvantages of digital imaging?
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fear of change
no film in hand trusting computers for storage unknown life expectancy of sensor initial set up cost |
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What is required components for digital imaging?
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software and computer with analogue to digital converter (ADC)
Monitor Printer Sensors or plates |
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How is digital imaging arranged?
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in a matrix of rows and columns
each cell of the image matrix is called a pixel or picture element each pixel has a row and column coordinates that identify its location in the matrix |
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Describe pixel size
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it varies from 20-70 microns
the smaller the pixel the higher the cost BUT the greater the resolution |
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With digital imaging, what is analogue data converted into?
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numerical data
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What happens to each pixel of digital imaging during xray?
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xray absorption generates voltage at each pixel
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What does ADC consist of
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sampling and quantification
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Sampling
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small range of voltage values are grouped together as a single value
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Quantization
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every sample is assigned a value
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How is voltage of output signal measured during digital imaging?
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it is measured and assigned a number from 0 (black) to 255 (white) according to the intensity of the voltage
this value stored in the computer represents the image |
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with digital imaging how many shades of gray can it translate?
how about with traditional xrays? the human eye/ |
numerical assignments translated 256 shades of gray in digital imaging
traditional radiographs differentiated 16-25 shades of gray the human eye can appreciate 32-64 shades of gray |
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Resolution
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the measure of small objects placed together
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resolution of film, CCD sensors, and PSP
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Film = 16-20 lp/mm
CCD = 8-10 lp/mm PSP = 6-8 lp/mm Film has the highest resolution and PSP has the lowest |
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With digital imaging what is used in place of film?
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plates or sensors
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2 ways to acquire direct image
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1. sensors
-CCD -CMOS 2. PSP plates |
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What does PSP stand for?
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photostimulable phosphor plates
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2 types of sensors
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1.CCD (charged couple device)
2.CMOS (complimentary metal oxide semiconductors) |
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how much less exposure do you get with digital sensors vs. D and E film?
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get 50-80% less exposure with sensors
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Thickness of digital sensors
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2.2-8 mm they are rigid with round edges
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describe CCD sensors
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solid state detectors made up of thin wafer of silicon crystals arranged in a pixel
the exposure creates electron hole pairs (greater exposure, greater e-hole pairs) e- are attracted to the positive potential and create charge pkts on each pixel emage is read by transferring each row of pixel charge from one to the the next pixel and is transferred to a ADC after sampling and quantification, the image is read |
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What should be used to increase xray absorption and effincy of CCD
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layer of scintillating material (gadolinium oxybromide cmpds or cesium iodide) coated on the CCD or coupled to the surface by fiberoptics
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detectors in CMOS
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silicon based semiconductors
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How are pixels read differently in CMOS than in CCD
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in CMOS each pixel is isolated and is directly connected to a transistor
electron holes are produced and charge is transferred to the transistor directly to a small voltage voltage is read by a frame grabber and then is stored and displayed as digital gray volume |
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Only company that makes CMOS sensor
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Schick
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What are some good things ahout sensors/
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first wireless direct digital imaging
no need for scanning or processing sensor instantly transmits images from mouth cable free sensors allow mobility hi level of image quality and reduced radiation exposure |
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What do PSP require?
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scanning
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What do PSP resemble?
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intraoral film in size, thickness, and rigidity
more flexible than sensors |
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What phosphor do PSP plates use?
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europium doped barium fluorohalide
the electrons in europium capture xray energy and are stored in metastable state |
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How are PSP plates image displayed?
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PSP plates are scanned with a red laser light scanner (600nm) which causes the plates to release energy in green spectrum (300-500nm)
light from the PSP is conducted to photomultiplier tube via fiberoptics photomultiplier tube converts light into electrical energy voltage signal is quantified by ADC and stored and displayed as digital imaging |
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what is added to PSP to allow only green light to be detected?
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a red filter at the photomultiplier tube is added to remove red light and only allow green light to be detected and converted into voltage
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when should PSP be processed?
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ASAD bc trapped e- are spontaneously released over time but PSP can be stored for 12-24 hrs and still retain ok image quality
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Is red safe light ok for exposed PSP?
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NO!!!!! bc PSP is most sensitive to red light spectrum
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2 types of scan systems for PSP plates
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1. stationary systems
2. rotating plate scans |
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How to erase and reuse PSP
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PSP is exposed to bright light to eliminate the ghost image from prior exposure
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ideal kVp for xray equiptment
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60-70 kVp
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what type of machine should CMOS and CCD be used with?
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CMOS and CCD detectors should preferabley by used with DC type intraoral machines with 1/100 sec exposure intervals for shorter exposure time
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What type of macine should PSP plates be used with?
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older AC xray machine
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what characteristic shoulc an xray generator have to be used with a solid state detector?
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low kVp (lower that 70kVp)
low mA (less than 5mA) accurate timer timer capable of producing very short and accurate times small focal spot a DC circuit |
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describe image processing with digital images?
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digital image can be altered by electronic image processing without making another exposure
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What can be done to process and edit digital image processing?
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contrast and brightness
image size measurement of structures image oritentation reduce noise/sharpen/smooth inversion pseudocolor notes copy flashlight |
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flashlight
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changes a small highlighted area to show trabeculae more clearly
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digital subtractoin
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two images of the same area taken at different intervals are required
shows the subtle differences between two images |
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average std digital image size
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200-400 KB
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image size of FMX
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8 MB
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image size of Pano
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5 MB
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image size of ceph
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6-8 MB
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describe teleradiology
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need a dedicated telephone line
does 56 KB/sec |
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what computer hardware is needed for digital imaging in dental office
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processor
plenty of RAM hard drive of 20 GB 56 kbps modem back up devices 600 dpi with transparency adapter color printer |
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what does DICOM stand for?
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digital imaging and communications in medicine
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Purpose of DICOM
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standardizes digital image formates
images can be transferred to remote sites |
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DICOM compliant
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system utilizes common file formats that are universally recognized
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